1. Technical Field of the Invention
The present invention relates to a DD (disk drive) motor in a magnetic disk drive, in particular, for use in 3.5-inch floppy disk drive.
2. Related Art
In a conventional DD motor 1 as shown in FIG. 8, a rotor 2 and a disk table 3 are separated by a frame 4 provided therebetween for shielding magnetic field. A printed board 5 is disposed on a surface of the frame 4 which faces onto the rotor 2. A coil is provided on a surface of the printed board 5. An induction magnetic field generated from the coil acts on a ring-like rotor magnet 7 disposed on an inner peripheral face of rim 6 in the rotor 2, thereby the rotor 2 is rotated.
A spindle shaft 8 in the rotor 2 is projected from the other surface of the frame 4 by piercing the printed board 5 and the frame 4, and the disk table 3 is fitted on the top end of the spindle shaft 8. When a magnetic disk, for instance 3.5-inch floppy disk (not shown), is set upon the disk table 3, a metal hub of the magnetic disk is attracted by the disk table 3 because the disk table 3 is made of magnet. Besides, a chucking roller 9 is mounted on one side of the top face of the disk table 3, wherein the chucking roller 9 is vertically movable with regard to the disk table and urged upwards in a normal state. When the hub of the magnetic disk is abutted against the disk table 3, the chucking roller 9 is sunk into the disk table 3.
Then while the disk table 3 is rotated by the rotation of the rotor 2, if the chucking roller 9 arrives at the position of a window formed in the hub, it is pushed upwards and is thereby engaged with the window. In this manner, the magnetic disk is chucked with the disk table 3 and thereby can be rotated with the rotor 2.
Thus in this kind of the disk drive, while the rotor starts to rotate and the chucking roller is engaged with the window of the magnetic disk hub, the disk table and the hub of the magnetic disk are rubbed on each other. Therefore, it is desirable that friction resistance of the disk table is less. Using such a material, however, the magnetic force of the disk table is decreased and there is fear of that it would not work as the chucking magnet.